Sealless rotary blood pump

ABSTRACT

An implantable rotary sealless blood pump includes a housing having an inlet tube on one end and an impeller casing on the other end. A rotor is mounted for rotation within the housing, with the rotor having an elongated shaft portion and an impeller attached to the shaft portion. The impeller is located within the impeller casing. Radial magnetic bearings are carried by the shaft portion and radial magnetic bearings are carried by the housing for maintaining the shaft portion of the rotor within the inlet tube of the housing. A rotor motor includes a plurality of permanent magnets carried by the impeller and a motor stator including an electrically conductive coil located within the housing. A ring of back iron is carried by the impeller to aid in completing a flux return path for the permanent magnets. A plurality of hydrodynamic thrust bearings are located outside of the axis of rotation of the rotor. The impeller uses large axially thick blade sectors with narrow blood channels extending through the impeller, to minimize hemolysis and to increase the working surface of the blades.

This application is a continuation of application Ser. No. 09/420,997,filed Oct. 20, 1999, now U.S. Pat. No. 6,234,998, which is acontinuation of application Ser. No. 09/108,434, filing date Jul. 1,1998, now U.S. Pat. No. 6,080,133 a division of application Ser. No.08/910,375, filed Aug. 13, 1997, now U.S. Pat. No. 5,840,070, which is acontinuation-in-part of application Ser. No. 08/603,536, filed Feb. 20,1996, now U.S. Pat. No. 5,695,471.

FIELD OF THE INVENTION

The invention relates generally to the field of blood pumps. Morespecifically, the invention pertains to continuous flow pumps of rotarydesign, suitable for permanent implantation in humans for use as chronicventricular assist devices.

BACKGROUND OF THE INVENTION

Thousands of heart patients who suffer from severe left ventricularheart failure could benefit from cardiac transplantation. However,owning to a shortage of donor hearts, most of these patients face aforeshortened life span characterized by frequent hospitalizations,severe physical disability, and death from congestive failure orcardiogenic shock. If a left ventricular assist device (“LVAD”) wereavailable for chronic use, many of these patients could be returned toprolonged and productive lives.

Prior art LVADs, now in clinical trials, provide a cyclic or pulsatingdelivery of blood, designed to emulate the natural pulsatile blood flowthrough the heart. This design approach has resulted in a variety ofanatomic and engineering problems. Cyclic delivery systems tend to bephysically large, making implantation difficult or impossible for somepatients. Cyclic delivery systems also employ artificial valves, havingspecial material, longevity, and performance requirements. All of thesecharacteristics make cyclic blood pumping device both complex andexpensive.

It is apparent that if the requirement of pulsatile blood flow iseliminated, the LVAD could be much smaller, simpler, and less expensive.Rotary pumps, whether of centrifugal or axial flow design, providesubstantially continuous liquid flow, and potentially enjoy a number ofthe listed advantages over cyclic delivery systems. However, the priorart has not developed a durable rotary blood pump, owing to uniqueproblems with the rotary pump's driveshaft seal. In a blood environment,such driveshaft seals have a short life, and contribute to a prematurefailure of the pump. Prior art driveshaft seals may also causeembolisms, resulting in a stroke or even death for the patient.

Accordingly, it is an object of the present invention to provide animproved rotary blood pump, by eliminating the necessity for adriveshaft seal;

It is a further object of the present invention to provide a compact,rotary blood pump using passive, magnetic radial bearings to maintain animpeller and its support shaft for rotation about an axis;

It is yet a further object of the present invention to provide a rotaryblood pump having bi-stable operation, in which the impeller and thesupport shaft shuttle as a unit, between two predetermined axialpositions;

It is another object of the present invention to provide blood immersedaxial thrust bearings which are regularly washed by fresh blood flow toprevent thrombosis from occurring;

It is yet another object of the present invention to provide a uniquethick bladed pump impeller, which houses both motor magnets and radialbearing magnets, and includes narrow, deep, blood flow passages;

It is yet another object of the present invention to provide a pumpimpeller which is effective pumping viscous liquids, such as blood, atlow flow rates, and which minimizes hemolysis of the blood by using onlya few pump impeller blades.

SUMMARY OF THE INVENTION

In accordance with illustrative embodiments of the present invention, arotary blood pump includes a housing and a pump rotor. A centrifugalpump impeller is attached to an impeller support shaft, or spindle, toform the pump rotor. The pump housing includes an elongated inlet tubesurrounding the shaft, and a scroll-shaped casing, or volute, with adischarge outlet, enclosing the impeller.

The shaft and the impeller are specially suspended within the housing.Radial magnetic bearings of passive design, maintain the support shaftand the impeller about a rotational axis. The magnetic bearing whichlevitates the shaft includes a plurality of permanent ring magnets andpole pieces arranged along surrounding portions of the inlet tube, and aplurality of permanent disc magnets and pole pieces within the shaftitself. Radially adjacent pairs of these magnets are of like polarity.One part of the magnetic bearing, which maintains the impeller about arotational axis, includes a plurality of permanent rod or arcuatemagnets disposed in spaced, circular relation around blade sectors ofthe impeller; another part of the bearing includes a pair of permanentring magnets outside the casing, on either side of the impeller.Adjacent portions of the rod and ring magnets are of opposite polarity.

The shaft and impeller are axially restrained by a magnetic andhydrodynamic forces in combination with mechanical thrust bearings, ortouchdowns. The magnets of the magnetic bearing in the inlet tube andshaft may be arranged in slightly offset axial relation, to produce atranslational loading force, or bias, along the longitudinal axis of therotor. This bias substantially counteracts the axial force resultingfrom the hydraulic thrust of the rotating impeller. However, thehydraulic thrust will vary as a function of the cardiac cycle andadditional restraints are desirable to ensure that pump operation isstable and controlled. For this purpose, a pair of blood immersed thrustbearings is provided. These thrust bearings may be located at either endof the rotor, although other arrangements are feasible.

One thrust bearing is included at the upstream end of the support shaft,and the other thrust bearing is located on the bottom, or downstreamside of the impeller. A spider within the inlet tube includes atouchdown, or thrust surface, against which the end of the shaftperiodically touches. Another touchdown is provided on an inner surfaceof the casing base, adjacent a downstream terminus of the impeller. Apredetermined amount of spacing is included between the two touchdowns,so as to allow the shaft/impeller assembly axially to shuttle back andforth, in response to the user's cardiac cycle. This shuttling motionwill produce a pumping action, frequently exchanging blood in thetouchdown area with fresh blood from the circulation. This pumpingaction minimizes the likelihood of blood thrombosis in the thrustregion, by maintaining the blood at an acceptable temperature and byshortening its residence time in the thrust bearing gap.

The impeller is of unique configuration and characteristics, owing tothe special requirements of the present application. Contrary toconventional centrifugal pump design, the present invention usesrelatively few impeller blades, generally resembling pie-shaped sectors.Moreover, the blades are made quite thick in an axial direction, havingdeep and narrow, arcuate channels between adjacent blades for thepassage of blood through the impeller. The substantial height of theblades provides a relatively large blade working surface, ensuringefficient pump operation. These structural features decrease hemolysisof the blood, while maintaining useful efficiency in a pump using so fewimpeller blades.

Sealed, hollow chambers are provided within the thick impeller blades toreduce the density of the impeller. These chambers reduce gravityinduced loads on the thrust bearings, which in turn reduces thelikelihood of thrombosis of the blood used to lubricate the bearings.

The thick impeller blades are also used advantageously to house magnetsused in the pump drive system. Torque drive is imparted to the impellerby magnetic interaction between arcuate, permanent magnetic segmentsimbedded within each impeller blade sector, and a circularelectromagnetic stator, affixed to the casing. Back-EMF sensing is usedto commutate the brushless motor stator, providing attractive andrepulsive forces upon the magnetic segments. A control unit and aportable power supply, worn on the user, power the pump drive system.The control unit allows the speed and drive cycle of the motor either tobe programmed or interactively determined by the user's physicalactivity or condition.

In certain embodiments of the invention, the motor includes a pluralityof permanent magnets carried by the impeller and a motor statorincluding an electrically conductive coil located within the housing. Aring of back iron is fixed to the casing to aid in completing a fluxreturn path for the permanent magnets and to decrease the axial thrustwhich results from the attraction of the motor rotor magnets toward themotor rotor stator. The impeller has a forward side facing the inlettube and a rear side downstream of the forward side. In one embodiment,the conductive coil of the motor stator is located adjacent the rearside of the impeller, and a stator back iron ring is located outside ofthe conductive coil, within the housing and fixed to the housing. In oneembodiment, a second ring of back iron is located on the forward side ofthe impeller and outside of the casing but inside of the housing, withthe second ring of back iron being fixed to the casing. In thatembodiment, a second motor stator having an electrically conductive coilis located on the forward side of the impeller outside of the casing butinside of the housing. In that embodiment, the second ring of back ironis located forward of the second motor stator.

In certain embodiments, a plurality of hydrodynamic thrust bearings arelocated outside of the axis of rotation of the rotor. The hydrodynamicbearings are wedge-shaped and, during rotation of the rotor andimpeller, the hydrodynamic bearings are separated from the casing by afluid film and are not in direct mechanical contact with the casing.

A more detailed explanation of the invention is provided in thefollowing description and claims, and is illustrated in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a left front perspective of the blood pump of the presentinvention;

FIG. 2 is a fragmentary, cross-sectional view of the pump of FIG. 1,showing a plurality of ring magnets comprising part of the magneticbearing assembly;

FIG. 3 is a fragmentary, cross-sectional view of the pump of FIG. 1,showing the shaft and an impeller;

FIG. 4 is a view as in FIG. 1, but with the shaft and impeller shownremoved from the housing;

FIG. 5 is a simplified, fragmentary, representation of a human heart,showing the pump implanted within the left ventricle of the heart;

FIG. 6 is a transverse, cross-sectional view of the housing, impeller,and impeller chamber, taken along the line 6—6, shown in FIG. 1;

FIG. 7 is a longitudinal, cross-sectional view of the pump, taken alongthe line 7—7, shown in FIG. 1;

FIG. 8 is a longitudinal, cross-sectional view of a simplified,schematic representation of the pump, showing respective polarities ofthe magnets and the pole pieces of the passive radial magnetic bearings,and the elements of the pump motor, including rotor magnets and a motorstator;

FIG. 8a is a schematic view, similar to FIG. 8, but showing anotherembodiment of the present invention;

FIG. 8b is a schematic view, similar to FIG. 8a, but showing anotherembodiment of the present invention.

FIG. 9 is a longitudinal, cross-sectional view of an impellerconstructed in accordance with the principles of the present invention;

FIG. 10 is an end view thereof, taken from the right side of FIG. 9;

FIG. 11 is a longitudinal, cross-sectional view of a simplified,schematic representation of another embodiment of the pump;

FIG. 11a is an enlarged view of the circled portion 11 a from FIG. 11;

FIG. 12 is a cross-sectional end view of the FIG. 11 pump with the endof the housing and casing removed for clarity;

FIG. 13 is a perspective view, partially broken for clarity, of theblood pump of FIG. 11;

FIG. 13a is a perspective view of a portion of FIG. 13, showing theslotted motor stator;

FIG. 13b is a perspective view, similar to FIG. 13a but showing aslotless motor stator.

FIG. 14 is another perspective view, partially broken for clarity, ofthe blood pump of FIG. 11;

FIG. 15 is a longitudinal, cross-sectional view of another embodiment ofthe pump;

FIG. 15a is an enlarged view of the circled portion 15 a from FIG. 15;

FIG. 16 is a cross-sectional end view of the FIG. 15 pump, with the endof the housing and casing removed for clarity;

FIG. 17 is a longitudinal, cross-sectional view of another embodiment ofa blood pump;

FIG. 17a is an enlarged view of the circled portion 17 a from FIG. 17;

FIG. 18 is a cross-sectional end view of the FIG. 17 pump, with the endof the housing and casing removed for clarity;

FIG. 19 is a longitudinal, cross-sectional view of another embodiment ofthe present invention;

FIG. 19a is an enlarged view of the circled portion 19 a from FIG. 19;and

FIG. 20 is a cross-sectional end view of the FIG. 19 pump, with the endof the housing and casing removed for clarity.

DETAILED DESCRIPTION OF THE DRAWINGS

Turning now to FIGS. 1-8 of the drawings, a sealless rotary blood pump11 includes a housing 12, having an elongated inlet tube 13 and animpeller casing or volute 14. A discharge tube 16 extends through thehousing to communicate with the interior periphery of casing 14. Tube 16has a tangential orientation with respect to a radius of the casing, foreffectively channeling the blood output from the pump.

A pump rotor 17 is located within housing 12, within casing 14, andincludes an elongated, right-circular cylindrical support shaft orspindle 18, attached to a disc-shaped impeller 19. Rotor 17 is mountedfor rotation about a longitudinal axis which extends both through shaft18 and impeller 19. It should be noted that the preferred embodimentdisclosed herein includes an impeller and a casing of centrifugaldesign. However, many of the structural features and aspects ofoperation of the present invention may also be adapted advantageously torotary blood pumps of axial flow design.

The pump 11 of the present invention includes a forward magnetic bearing21 and a rearward magnetic bearing 22 to levitate rotor 17 and maintainit in proper radial alignment with respect to its longitudinal axis. Aradial magnetic bearing construction is shown in U.S. Pat. No.4,072,370, issued to Wasson. The '370 Patent is hereby expresslyincorporated by reference. The forward magnetic bearing 21 herein may beconstructed entirely in accordance with the teachings of the '370Patent. However, several simplifications and improvements to theconstruction shown in the '370 Patent are disclosed herein. For example,it has been determined that the radially polarized ring magnets(numerals 44 and 46) of the '370 device, are not necessary forsuccessful practice of the invention herein. In addition, as will beexplained below, the axially magnetized ring magnets (numeral 22) of the'370 device may advantageously be replaced with axially magnetized discmagnets for purposes of the present invention.

Accordingly, the forward magnetic bearing 21 includes a plurality ofrings, comprising ferromagnetic pole pieces 23 and axially polarizedpermanent magnets 24. As shown most clearly in FIGS. 7 and 8, polepieces 23 and magnets 24 are arranged in contingent, alternatingfashion, and are located between outer sidewall 26 and inner sidewall 27of inlet tube 13. The polarization of opposing magnets is the same,inducing an identical polarization into a respective pole piecetherebetween. A combination of high strength adhesive and surroundingtube sidewalls, maintains the arrangement of magnets and pole pieces incontingent relation, despite strong magnet forces attempting to urge therings apart.

Forward magnetic bearing 21 also includes a plurality of discs,comprising ferromagnetic pole pieces 28 and axially polarized permanentmagnets 29. Pole pieces 28 and magnets 29 are also arranged incontingent, alternating fashion, so as to form a magnetic structurewhich mirrors the polarity and axial position of respective pieces andmagnets of the surrounding rings. This magnetic structure is firstassembled and secured together using high strength adhesive, and is theninstalled within the hollow volume of shaft or spindle 17. The magneticpolarizations and repulsive forces produced by the magnets and the polepieces of forward magnetic bearing 21 are such that magnetic levitationof support shaft 18 results.

To provide additional radial restraint for rotor 17, rearward magneticbearing 22 is also provided. Bearing 22 includes a first ring magnet 31mounted on an outer wall of casing 14, and a second ring magnet 32imbedded within a circular casing base 33. The bottom portion of casing14 is attached and sealed to base 33, to form a fluid imperviousenclosure for impeller 19 (see FIG. 7). Both magnets 31 and 32 areaxially polarized, but each has a different polarization facing impeller19. Bearing 22 also includes a plurality of rod magnets 34, transverselyextending from an upper face portion 36 to a lower face portion 37 ofimpeller 19. Rod magnets 34 are arranged in spaced, circular fashion,adjacent an outer periphery 38 of impeller 19. The polarizations betweenthe ends of magnets 34 and the adjacent surfaces of magnets 31 and 32are respectively opposite, creating attractive, but equal and oppositemagnetic forces acting on the impeller. It can be seen that radialmovement of the impeller (deflection from the axis of rotation) willresult in a restoring force due to the attraction between the magnets 34towards magnets 31 and 32. The magnetic force in the axial directionwill largely be counterbalanced to the opposing magnetic attraction ofmagnets 34 to magnet 31 and magnets 34 to magnet 32. However, the actionof the magnetic force in the axial direction would not be restoring.

It should also be noted that other configurations, locations, numbers,and polarization orientations may be used for the components formingrearward magnetic bearing 22. For example, magnets 34 may be arcuatesegments, rather than rods. Also, the polarizations of the magnets 31,32, and 34 may be arranged to effect respective repulsive forces, ratherthan the attractive forces specifically disclosed herein. In thismanner, referring to FIGS. 8a and 8 b, the south pole of magnets 34would be adjacent the south pole of magnet 31 and the north pole ofmagnets 34 would be adjacent the north pole of magnet 32. For themagnets to be restoring in the radial direction, the magnets would haveto be offset. To this end, in the FIG. 8a embodiment magnets 34 would bemore outward radially than magnets 31 and 32. Alternatively, in the FIG.8b embodiment magnets 34 are radially inside the radial dimension ofmagnets 31 and 32. If a repulsive configuration is used, as illustratedin FIGS. 8a and 8 b, the action of the magnetic force would be restoringin both the radial and axial direction.

Although the drawings show magnets 32 and 34 as if portions thereof aredirectly immersed in blood, in actual practice, a thin-wallednon-magnetic jacket or a plastic coating would be placed over theseportions, to prevent contact between the magnets and the blood. Suchcontact, if it were allowed, would likely cause an undesirable chemicalreaction, to the detriment of the blood. However, for clarity, thereferenced jacket or coating, is not shown in the drawings.

To provide mechanical limitations on axial, translational excursions ofthe rotor, a first thrust bearing 39 and a second thrust bearing 41 areprovided. First thrust bearing 39 includes a threaded plug 42, installedwithin casing base 33. Plug 42 is screw adjustable along thelongitudinal axis of rotor 17, and includes a recessed bearing surface43. Surface 43 is contoured to accommodate a corresponding bearing tip44, in the lower face portion of impeller 19. It should be noted thatthe particular configuration of bearing 39 is not critical, and planarbearing surfaces may alternatively be used in this application.

Second thrust bearing 41 is secured within the blood entry end of inlettube 13, and includes a spider 46, adjustment knob 47, and ball 48.Rotation of knob 47 will translate ball 48 along the longitudinal axisof rotor 17.

Alternative locations and constructions for second thrust bearing 41 arealso contemplated. For example, an annular thrust bearing surface couldbe provided on the inner wall of casing 14, adjacent the upper faceportion 36 of impeller 19. In this arrangement, portion 36 wouldslidably contact the annular thrust bearing surface. By eliminatingspider 46 and the associated components of the upstream thrust bearing,the possibility of blood deposits forming on these structures would beeliminated.

It will be appreciated that thrust bearings 39 and 41 are effective notonly to provide limit stops to axial movement of rotor 17, but also toadjust certain operational aspects of the pump. In the drawings, theupstream end of support shaft 18 is shown in contact with ball 48.However, this will not always be the case during the course of operatingthe pump. For example, it is desirable for the two thrust bearings to beadjusted so that the distance between them, is slightly greater than theoverall length of the rotor. This will allow the rotor to “shuttle”,back and forth between the axial constraints provided by the thrustbearings with each cardiac cycle of the user. Each such cycle willproduce a pumping action, bringing fresh blood into the touchdown, orthrust bearing area.

The present invention does not use a journal bearing to restrain therotor. Of necessity, a journal bearing radially encases at least aportion of the rotor's support shaft or spindle. It is within this thin,annular volume between the shaft and the bearing surface, wherethrombosis can occur in prior art devices as a consequence of heat andexcessive residence time within the bearing. The bi-stable operation ofthe pump and rotor of the present invention, continuously flushes theblood around each thrust bearing, avoiding thrombosis effects of priorart journal bearings.

There is also an important physical relationship which exists betweenthe rotor and the magnetic bearings of the device disclosed herein. Thisrelationship is established and maintained by proper axial placement ofthe adjustable thrust bearings. In operation of the pump, the pressuregradient produced by the rotating impeller imparts an upstream axialforce on the rotor. This force needs to be substantiallycounterbalanced, to ensure that cardiac pulses will create sufficientpressure variances through the pump, to effect bi-stable operation. Byadjusting the axial relationship of the pole pieces 23 and the magnets24 with respect to the pole pieces 28 and magnets 29, a downstream axialforce will be produced. Since the forces within forward magnetic bearing21 are repulsive, the desired downstream loading or bias will beeffected when the magnets and pole pieces within the shaft aretranslated slightly downstream from the magnets and pole pieces in theinlet tube (See, FIGS. 7 and 8). Thus, second thrust bearing 41 iseffective to shift, or offset the rotor downstream a sufficient amountso the resultant, repulsive magnetic forces substantially counterbalancethe hydrodynamic axial force produced by the rotating pump impeller.

We can now turn to the special design considerations and operationalcharacteristics of impeller 19. As will be noted particularly in FIG. 6,the impeller includes a plurality of large blade sectors 49. Owing toits relatively high viscosity and susceptibility to damage from heat andmechanical action, blood is a uniquely difficult liquid to pump.

It is generally preferable in a large centrifugal pump, to have asubstantial number of thin, sharp impeller blades with relatively largevoids or passages, between the blades, for the passage of low viscosityliquid. However, such a conventional design is not desirable, for asmall centrifugal pump which has to pump a viscous liquid, such asblood.

When blood flows axially into the leading edges of impeller blades ittends to be damaged by the mechanical action and turbulence associatedwith the impeller blades. Thus, one of the design considerations of thepresent invention is to reduce such hemolysis, by minimizing the numberof impeller blades and leading edges.

To maintain efficiency in a small pump with so few blades, the effectiveworking area of the blades needs to be increased. This was accomplishedin the present design by modifying the size and configuration ofconventional blades in two significant aspects. First, blade sectors 49are made relatively wide or expansive through a rotational aspect (seeFIG. 6). In other words, the outer periphery of each blade sector 49assumes approximately 80 to 85 degrees of rotation. It should be notedthat an alternative design contemplated herein includes only two bladesectors, each of which assumes approximately 175 degrees of rotation. Ineither case, the width of the impeller blade sectors of the presentinvention differ significantly from known prior art blades.

The second modification pertains to the thickness or height of the bladesectors. As shown particularly in FIGS. 4 and 7, blade sectors 49 arerelatively thick in an axial direction. As a consequence of thesemodifications, a narrow and deep impeller blood flow path or passageway51 is defined between adjacent edges of blade sectors 49. By increasingthe thickness of the blade sectors and narrowing the blood passageway,the ratio between the area of working surface of the blades and thevolume of the passageway is increased. Also, the average distance of theliquid in the passageway from the working surface of the blades isdecreased. Both of these beneficial results provide a small pump forblood which has few blades for damaging blood, yet maintains acceptableefficiency.

The size and configuration of the impeller blades also allows thestructural integration of a number of features directly within theimpeller 19. For example, the previously discussed rearward magneticbearing 22 includes a plurality of rod magnets 34 of considerablelength. Owing to the thickness of the blade sectors, these magnets arereadily accommodated within the sectors. The sectors may also beprovided with respective hollow chambers 52, to reduce the mass of theimpeller and the gravity induced loads on the thrust bearings (see, FIG.6).

Lastly, a brushless rotor motor 53 includes arcuate magnetic segments54, imbedded within the upper face portion 36 of blade sectors 49. Asdiscussed above, the portions of segments 54 which would otherwise be influid communication with the pumped blood, are encased in a jacket or acoating (not shown) to prevent any chemical reaction between the bloodand the magnetic segments. Making reference to FIGS. 6 and 8, segments54 have alternating orientations in their polarities, and are directedtoward an adjacent motor stator 56. Included within stator 56 arewindings 57 and a circular pole piece or back iron 58, mounted on theouter surface of impeller casing 14. Windings 57 are interconnected bymeans of percutaneous wires to a controller 59 and a power supply 61, asshown in FIG. 5. Alternative to using wires, transcutaneous powertransmission could be used. It is contemplated that controller 59 andpower supply 61 may be worn externally by the user, or alternatively,they may be completely implanted in the user.

Controller 59 may include circuitry as simple as a variable voltage orcurrent control, manually adjusted or programmed to determine therunning rate of pump. However, controller 59 may also have interactiveand automatic capabilities. For example, controller 59 may beinterconnected to sensors on various organs of the user, automaticallyand instantaneously to tailor operation of the pump to the user'sphysical activity and condition.

The windings 57 are energized by the electrical output of controller 59to produce an electromagnetic field. This field is concentrated by polepiece 58, and is effective to drive magnets 54 and the rotor 17, inrotary fashion. The back EMF resulting from the magnets 54 passing bythe windings is detected by the controller. The controller uses thisback EMF voltage to continue generation of the electromagnetic field insynchronism with further rotation of the rotor. Brushless operation ofthe motor 53 is effected, then, by electromagnetic interaction betweenthe stator and magnets imbedded within the pump's impeller blades.

Motor 53, with windings 57 and pole piece 58, together with magnets 54,function not only to transmit torque but also provide a restoring radialmagnetic force that acts as a radial bearing. As illustrated in FIGS. 7and 8, magnets 54 are carried by blade sectors 49 and are positioned inradial alignment with pole piece 58. The magnets 54 have attraction withthe iron pole piece 58 of the stator. Any attempt to deflect theimpeller radially produces an increasing restoring force between thepole piece 58 and the magnets 54 which would cause the impeller toreturn to a neutral position.

Rotation of the rotor 17, including shaft 18 and impeller 19, causesblood to flow through inlet tube 13 in the direction of arrows 62. Theblood continues its path from the upper edge of passage 51 to theinterior of casing 14. Discharge tube 16 allows the blood to be expelledfrom the casing an into the user's cardiovascular system.

Anatomical placement of the pump 11 is shown in FIG. 5. The simplifiedrepresentation of a human heart 63, includes a left ventricle 64 and anaorta 67. The inlet tube 13 serves as the inflow cannula and is placedinto the apex of the left ventricle 64. An arterial vascular graft 66 isconnected on one end to tube 16 and on the other end to the aorta 67through an end to side anastomosis.

The centrifugal design of the pump allows a considerable amount offlexibility during implantation. Owing to the axial inflow and radialoutflow of the pump, a 90 degree redirection of the blood is effectedwithout the necessity of a flow-restrictive elbow fitting. Moreover, thepump can be rotated on its longitudinal axis to adjust the orientationof the discharge tube and minimize kinking and hydraulic losses in thevascular graft. Good anatomic compatibility is possible since the pumpcasing is compact and disc-shaped, fitting well between the apex of theheart and the adjacent diaphragm.

In a specific example although no limitation is intended, referring toFIG. 7, blood flow path 62 a is 0.06 inch to 0.1 inch in thickness. Thefluid gap 70 comprising the clearance between the impeller and thehousing is 0.005 inch to 0.02 inch. The impeller diameter is 1.0 inch to1.5 inch. The rotor diameter is 0.025 inch to 0.4 inch. The outsidediameter of the flow annulus is 0.35 inch to 0.55 inch. The outerdiameter of the housing adjacent the forward end of the pump is 0.85inch to 1.25 inch. The axial length of the entire pump is 1.75 inch to3.0 inch. The axial length of the rotor spindle is 1.0 inch to 1.5 inchand the axial length of the impeller is 0.2 inch to 0.5 inch. By using athick impeller (having a long axial length) the fluid gap 70 can belarger and still provide a highly efficient pumping action.

Enlarged views of an impeller used in the pump of the present inventionare set forth in FIGS. 9 and 10. Referring to FIGS. 9 and 10, animpeller 74 is shown therein having a number of blade sectors 76, 78 and80. Blade sectors 76 and 78 are separated by slot 82; blade sectors 78and 80 are separated by slot 84; and blade sectors 80 and 76 areseparated by slot 86. By utilizing blade sectors 76, 78 and 80 that arerelatively thick in the axial direction, narrow and deep impeller bloodflow paths are formed by slots 82, 84 and 86 between the adjacent edgesof the blade sectors. By increasing the thickness of the blade sectorsand narrowing the blood passageway, the ratio between the area ofworking surface of the blades and the volume of the passageway isincreased. Also, the average distance of the liquid in the passagewayfrom the working surface of the blades is decreased. Both of thesebeneficial results allow a small pump for blood which has less bladesfor potentially damaging blood, yet the small pump maintains acceptableefficiency.

As a specific example although no limitation is intended, the diameterof the impeller is 1 inch to 1.5 inch, the blade depth bd (FIG. 9) is0.2 inch to 0.5 inch, the magnet width mw (FIG. 9) is 0.15 inch to 0.3inch, the spindle diameter sd (FIG. 9) is 0.25 inch to 0.5 inch, and theinner diameter id (FIG. 9) of the impeller inlet is 0.45 inch to 0.6inch. The width w of the slots (see FIG. 10) is approximately 0.075 inchand preferably ranges from 0.05 inch to 0.2 inch. The outlet angle a(FIG. 10) preferably ranges between 30° and 90°.

Another benefit of the thick impeller is the ability to utilize magneticpieces 88 that are inserted in a manner enabling the stators to be onopposite sides of the impeller. Referring to FIGS. 11, 11 a, 12, 13 and14, the blood pump 11′ shown therein is similar in many respects toblood pump 11 illustrated in FIGS. 1-8, and includes housing 12 havingan elongated inlet tube 13 and a scroll-shaped impeller casing or volute14. A discharge tube 16 extends through the housing to communicate withthe interior periphery of casing 14. Tube 16 has a tangentialorientation with respect to a radius of the casing, for effectivelychanneling the blood output from the pump.

Pump rotor 17 is located within housing 12, within casing 14, andincludes an elongated, right-circular cylindrical support shaft orspindle 18, attached to impeller 74. Rotor 17 is mounted for rotationabout an longitudinal axis which extends both through shaft 18 andimpeller 74.

The magnetic bearings for levitating rotor 17 and maintaining it inproper radial alignment with respect to its longitudinal axis are notspecifically shown but may be identical to those illustrated in the pumpembodiment of FIGS. 1-8 and described above.

In the FIGS. 11-14 embodiment, a first motor stator 90, comprisingconductive coils or motor windings 91, is located at the rear ofimpeller 74. A ring of back iron 92 is located behind windings 91 and,as illustrated in FIG. 11, first motor stator 90 and back iron 92 arefixed between housing 12 and casing 14.

A second motor stator 94, comprising windings 95, is positioned on theforward side of impeller 74. As illustrated in FIG. 11, windings 95 arefixed to casing 14 and a ring of back iron 96 is positioned forward ofwindings 95. As illustrated in FIGS. 13, 13A and 14, back iron 92 andback iron 96 have teeth 98 which extend into the stator windings to formthe stator iron. Thus the windings 95 wrap around the teeth 98 in theintervening slots 99 (See FIG. 13a). In the FIG. 13b embodiment, aslotless motor stator is illustrated. In that embodiment, the windings91 are fixed to the back iron 96 and there are no teeth extending intothe stator windings.

It can be seen that the motor stators 90 and 94 are placed on oppositesides of casing 14 such that each is adjacent to the pole faces of themotor rotor magnets 98. Back iron 92 and back iron 96 serve to completea magnetic circuit. The windings 91 and 95 of the stators 90, 94 can bein series or each stator 90, 94 can be commutated independent of theother. There are several advantages to this approach:

First, as long as the pole faces of the motor rotor magnets are centeredbetween the faces of the motor stators, the net axial force will berelatively low.

Second, the radial restoring force which results from the attractiveforce of the motor rotor magnets to the motor stators will be nearlytwice as large as the restoring force with only one stator. The totalvolume and weight of the motor will be smaller than a single statordesign.

Third, the dual stator design is adapted to provide system redundancyfor a fail safe mode, since each stator can be made to operateindependently of the other in the case of a system failure.

Fourth, hydrodynamic bearings can be located on the surface of theimpeller to constrain axial motion and to provide radial support in thecase of eccentric motion or shock on the device. Referring to FIGS. 11and 11a in particular, hydrodynamic bearings in the form of raised pads100, 101 and contact surfaces 102 and 103 are illustrated. Suchhydrodynamic bearings are symmetrically located about the impeller asillustrated in FIG. 13, in which raised pads 100 are shown.

The raised pads could be rectangularly-shaped or wedge-shaped and arepreferably formed of hardened or wear resistant materials such asceramics, diamond coatings or titanium nitride. Alternatively, theraised pads may be formed of a different material having an alumina orother ceramic coating or insert.

The raised pads are carried by either the impeller or the casing, or anattachment to the casing. In the FIGS. 11 and 11a embodiment, the raisedpads 100 are carried by the impeller and the raised pads 101 are carriedby a cup-shaped member 104 that is fastened to the casing. Cup-shapedmember 104 is utilized as a reinforcement for the casing which would notbe structurally stable enough to carry the raised pads itself.

The hydrodynamic bearings are formed by a raised pad spaced from acontact surface by the blood gap. Although at rest there may be contactbetween the impeller and the casing, once rotation begins eachhydrodynamic bearing is structured so that during relative movementbetween the raised pad and the contact surface the hydrodynamic actionof the fluid film produces increased pressure within the bearing gapwhich forces the raised pad and the contact surface apart.

Depending upon the location of the hydrodynamic bearings, they can aidin axial support, radial support or both axial and radial support. Forexample, if the bearings are perpendicular to the rotational axis, theyaid primarily in axial support but if they are at an angle with respectto the rotational axis, they aid in both radial and axial support. Inthe embodiment of FIGS. 11-14, the hydrodynamic bearings are positionedoutside the axis of rotation, as illustrated.

In the FIGS. 15-16 embodiment, there is a single axial motor and thestator 90 is located at the rear end of impeller 74. Stator 90 compriseswindings 91, and a ring of back iron 92 is located downstream ofwindings 91. The motor stator 90 and back iron are fixed between casing14 and housing 12.

In the FIGS. 15-16 embodiment, a ring of back iron 106 is placed in theimpeller, in axial alignment with the magnets, such that it completesthe flux return path for the motor rotor magnets in the impeller. Thuswhile motor stator 90 and back iron 92 are located downstream of theimpeller and outside of casing 12, back iron 106 is located within theimpeller and within the casing 12. Using back iron to complete themagnetic circuit in this manner increases the overall efficiency of themotor.

Referring to the embodiment of FIGS. 17-18, a motor stator 90 and backiron 92 are provided at the rear end of impeller 74 as with the FIGS.9-14 embodiments, but another ring of back iron 108 is placed outsidepump casing 12 on the front side of the impeller and is fixed to thecasing. Back iron ring 108 serves two purposes. First, it serves to helpcomplete the flux return path for the motor rotor magnets. Second, theattractive force between the motor rotor magnets and the ring of backiron 108 substantially reduces the net axial force produced by theattraction of the motor rotor magnets for the stator iron. Third, thering of back iron significantly increases the radial restoring forcecompared to just the interaction between the motor rotor magnets and thestator iron.

Although the FIGS. 1-18 embodiments utilize an axial flux gap motor, inthe FIGS. 19-20 embodiment a radial flux gap motor is utilized. To thisend, a ring-shaped structure is placed on either side of the impeller tohouse a series of motor rotor magnets (an even number) oriented suchthat the magnetic poles of the motor rotor magnets are radially, andalternately, aligned. The inner diameter of the magnets is located onthe surface of a ring of back iron to provide a flux return path. On theopposite end of the impeller, passive radial magnetic bearings are used.

It can be seen that in the FIG. 19-20 embodiment the motor rotor magnets110 are radially aligned. Radially within the motor rotor magnets 110 isa ring of back iron 112. The inner diameter of magnets 110 are locatedon the surface of back iron ring 112 (see FIG. 20) to provide a fluxreturn path. The motor rotor magnets 110 and ring of back iron 112 arecarried by the impeller, within the casing 14. Outside of the casing 14there is radially positioned a ring-shaped stator 114 with motorwindings 116.

A number of axial permanent magnets 120 are carried by the impeller, atits rear end. A number of axial permanent magnets 122 are fixed to thecasing 14 and housing 12, downstream of and partially offset from,magnets 120. Magnets 120 and 122 serve as passive magnetic bearings forthe impeller.

There are two significant differences from axial flux gap motors byusing the radial flux gap motor. First, there is very little axial forceproduced by the interaction between the motor rotor magnets and thestator. Second, there is no restoring force with the radial flux gapmotor. Radial support is provided by mechanical bearings or dedicatedradial magnet bearings.

It will be appreciated, then, that I have provided an improved seallessblood pump including magnetic bearings and thrust bearing suspension tominimize thrombosis, and an impeller having a blood flow paththerethrough which is calculated to minimize hemolysis.

Various elements from the FIGS. 1-8 embodiment can be used in the FIGS.11-20 embodiments. For example, magnets 34 illustrated in FIGS. 3 and 4could be used in impeller 74 of the FIGS. 11-20 embodiments. Also, rotor18 of the FIGS. 11-20 embodiments could be supported using front thrustbearings such as thrust bearing 41 of the FIGS. 1-8 embodiment. Variousother elements may be employed in the FIGS. 11-20 embodiments from theFIGS. 1-8 embodiment.

Although illustrative embodiments of the invention have been shown anddescribed, it is to be understood that various modifications andsubstitutions may be made by those skilled in the art without departingfrom the novel spirit and scope of the present invention.

What I claim is:
 1. A sealless rotary blood pump comprising: a pumphousing; a rotor comprising an impeller having a hydrodynamic bearingsurface; a motor including a plurality of magnets carried by saidimpeller and a motor stator including an electrically conductive coillocated within said housing; and hydrodynamic bearings symmetricallylocated about the impeller.
 2. The blood pump of claim 1, and furthercomprising a ring of back iron carried by said impeller, said back ironin axial alignment with said magnets.
 3. The blood pump of claim 2,wherein said conductive coil and said back iron are fixed within saidhousing at rear end of said impeller in alignment with said magnets. 4.The blood pump of claim 1, wherein said magnets are radially aligned. 5.The blood pump of claim 1, and further comprising permanent magneticbearings located at rear side of said impeller.
 6. The blood pump ofclaim 1, wherein said impeller is comprised of a disk shaped memberhaving an upper face portion, a lower face portion and having aplurality of blade sectors, each of said blade sectors being separatedfrom an adjacent sector by a channel extending from said upper faceportion to said lower face portions.
 7. A sealless rotary blood pumpcomprising: a pump housing; an impeller; a motor including a pluralityof magnets carried by said impeller, a first motor stator including anelectrically conductive coil and a second motor stator including anelectrically conductive coil, said first and second motor statorslocated within said housing and on opposite sides of said impeller; anda plurality of hydrodynamic thrust bearings located outside the axis ofrotation of said impeller.
 8. The blood pump of claim 7, and furthercomprising a first ring of back iron to aid in completing a flux returnpath for said magnets, said ring of back iron fixed within said housingrearwardly from said impeller.
 9. The blood pump of claim 8, and furthercomprising a second ring of back iron to aid in completing a flux returnpath for said magnets, said second ring of back iron fixed within saidhousing on an opposite side of said impeller than said first ring ofback iron.
 10. The blood pump of claim 7, wherein said impeller iscomprised of a disk shaped member having an upper face portion, a lowerface portion and having a plurality of blade sectors, each of said bladesectors being separated from an adjacent sector by a channel extendingfrom said upper face portion to said lower face portions.
 11. The bloodpump of claim 10, wherein said impeller has a diameter between 1 inchand 1.5 inch.
 12. The blood pump of claim 11, wherein said impellerblade depth is between 0.2 inch and 0.5 inch.
 13. The blood pump ofclaim 12, wherein said channel has a width between 0.5 inch to 0.2 inch.14. A sealless blood pump comprising: a pump housing having an inlet andan outlet; a rotor comprising an impeller having hydrodynamic bearingsurfaces; hydrodynamic bearings symmetrically located about theimpeller; and a rotor comprising a plurality of permanent magnetscarried by said impeller and a motor stator including an electricallyconductive coil and a pole piece located within said housing.
 15. Theblood pump of claim 14 and further comprising a ring of back ironcarried by said impeller.
 16. The blood pump of claim 15, wherein saidconductive coil and said back iron are fixed within said housing at rearend of said impeller and in alignment with said permanent magnets. 17.The blood pump of claim 14, and further comprising permanent magneticbearings located at rear side of said impeller.
 18. The blood pump ofclaim 14, wherein said impeller is comprised of a disk shaped memberhaving an upper face portion, a lower face portion and having aplurality of blade sectors, each of said blade sectors being separatedfrom an adjacent sector by a channel extending from said upper faceportion to said lower face portions.
 19. A sealless blood pumpcomprising: a pump housing having an inlet and an outlet; an impellerhaving a hydrodynamic bearing surface; a motor including a plurality ofmagnets carried by said impeller and a first motor stator including anelectrically conductive coil and a pole piece located within saidhousing wherein said pole piece comprise teeth extending from a ring ofback iron.
 20. The blood pump of claim 19, and further comprising aplurality of hydrodynamic thrust bearings.
 21. The blood pump of claim19, and further comprising permanent magnetic bearings located at rearside of said impeller.
 22. The blood pump of claim 19, wherein saidmagnets are radially aligned.
 23. The blood pump of claim 19, andfurther comprising a second motor stator including an electricallyconductive coil, said first and second motor stators located within saidhousing and on opposite sides of said impeller.
 24. The blood pump ofclaim 19, and further comprising a ring of back iron disposed withinsaid housing, said back iron in alignment with and completing a fluxreturn path for said permanent magnets.
 25. The blood pump of claim 19,and further comprising hydrodynamic bearings symmetrically located aboutthe impeller.